1. Field of the Invention
This invention relates to heat fixing rolls useful as transfer rolls, heating rolls and pressure rolls in plain paper copiers (PPC), laser beam printers (LBP), and facsimile machines.
2. Prior Art
Through the years, facsimile machines, copiers, and computer systems have increased in speed. For increasing the time taken for fixation in a fixing section, attempts have been made to reduce the hardness of rubber material to insure a fixing width or nip width in the high-speed systems of today. Fixing rolls are required to insure a sufficient contact area (also known as nip width) under low pressure and at high speeds in order to have a satisfactory fixing function. Also fixing rolls should be fully durable.
Conventional fixing rolls satisfying these requirements include multi-layer rolls comprising a roll base having a primer coated thereon, a lower layer of sponge obtained by curing a millable silicone rubber with an organic peroxide catalyst, and a surface layer obtained by coating an addition reaction type liquid silicone rubber or condensation reaction type liquid silicone rubber. Rolls formed solely of addition reaction type liquid silicone rubber are also used.
However, the multi-layer sponge rolls have the drawback that due to uneven cell distribution in the sponge, non-uniform pressure is applied to cause variations in the fixed images. The multi-layer sponge rolls having a surface layer of an addition or condensation reaction type liquid silicone rubber coated thereon and the rolls formed solely of addition reaction type liquid silicone rubber are unsatisfactory in abrasion resistance to paper and durability of toner release. Additionally, a system of feeding silicone oil to a silicone roll fails to secure a constant nip width due to swelling of the silicone roll with the silicone oil.